THE THUMB IN MONKEYS 
appears, according to the traveller Bates, to be easily 
accomplished by Cebus albifrons. Their agility can be 
readily studied at the Zoo, though the limited range for 
leaping and climbing renders it a little difficult to 
compare, and award the palm satisfactorily. 
The general characters of the Platyrrhine form of 
monkey can be as well studied in these monkeys as in 
any other. The widely separated forwardly and not 
downwardly directed nostrils, the prehensile tail, are 
all obvious ; but it will be hardly possible to note in 
the living monkey the thirty-six teeth, which are four 
in excess of the teeth of the monkeys of the Old World, 
including man. 
SPIDER MONKEY 
There are several kinds of spider monkey, perhaps 
ten. But they all agree in representing the Platyrrhine 
characters, or at least one of them, in a quite exaggerated 
fashion. The prehensile tail is eminently prehensile, 
its tip naked beneath to afford a securer clutch ; it is 
never at rest even when not in use as a “‘ fifth hand” ; 
perpetually does it explore the objects lying above the 
monkey’s back, like the restless tentacle of an anemone. 
The name spider monkey refers to the straddling and 
spider-like appearance presented when one of these 
monkeys is grasping various objects with hands, feet, 
and tail widely divaricated and radiating from the 
small body in the centre. The spider monkeys of the 
New World suggest the gibbons of the Old. In many 
monkeys the thumb has become somewhat rudimentary ; 
in Ateles, as the spider money genus is termed, it has 
often disappeared. But the reason for this, or at least 
a reasonableness in the fact, is evidenced when it is 
considered that the hand of these and many monkeys is 
of the nature of a hook to grasp temporarily a branch 
40 
